The present invention relates to a semiconductor device, and more particularly to a semiconductor device including a magnetic tunnel junction (MTJ) device.
A dynamic random access memory (DRAM), which is one of the widely used semiconductor memory devices, has features of high operation speed and high integration. However, the DRAM is a volatile memory device which loses data, when a power is off, and performs a refresh process to prevent loss of stored data, even when the power is on. Meanwhile, a flash memory is a non-volatile memory device and may be manufactured in high integration, while having a relatively low operation speed. As compared with the DRAM and the flash memory, a magneto-resistance random memory device (MRAM) has features of non-volatility, high operation speed, and high integration (scalability).
The MRAM is a non-volatile memory device where data is stored by magnetic storage elements having a different resistance depending on magnetic field changed between ferromagnetic plates. The magnetic storage element is a component including two ferromagnetic plates separated by an insulating layer. If polarities of the two ferromagnetic plates are parallel (the same), resistance of magnetic storage element is minimized. On the other hand, if polarities of the two ferromagnetic plates are opposite, the resistance is maximized. The MRAM device stores data based on cell's resistance changed depending on magnetization of ferromagnetic plates in the magnetic storage element. As a magnetic storage element, a Magnetic Tunnel Junction (MTJ) is widely used.
In the MRAM, the MTJ generally includes a stacked structure of a ferromagnetic layer, an insulating layer, and another ferromagnetic layer. When electrons pass through an insulating layer serving as a tunneling barrier from a first ferromagnetic layer, the degree of tunneling the insulating layer by the electrons is determined by magnetic direction of second ferromagnetic layer. If two ferromagnetic layers have the same polarity (parallel magnetic direction), amount of current tunneling the insulating layer is maximized. On the other hand, if two ferromagnetic layers have opposite magnetic direction, amount of current is minimized. For example, when resistance based on the tunneling current is high, information stored in the MTJ may be recognized as a logic level “1” (or “0”). If the resistance is low, information may be recognized as a logic level “0” (or “1”). Here, one of two ferromagnetic layers is called a pinned layer because its polarity is set to particular value, but the other is called a free layer because its polarity may be changed depending on magnetic field or supplied current.
However, there are some limits in manufacturing the MTJ device. First, it is not easy to make stacked patterns of a ferromagnetic layer, an insulating layer, and another ferromagnetic layer. Also, if sides of stacked patterns are exposed after patterning process, by-products are likely to adhere to the exposed surface of stacked patterns to cause a short circuit.